Patients who are incompetent need a surrogate decision maker to make treatment decisons on their behalf. One of the main ethical questions that arise in this context is what standard ought to govern such decision making. According to the Substituted Judgment Standard , a surrogate ought to make the decision that the patient would have made, had he or she been competent. Although this standard has sometimes been criticized on the grounds of being difficult to apply, it has found wide appeal, since it it is alleged to protect incompetent patients? right to autonomy. The main purpose of the thesis is to evaluate SJS, from a conceptual and ethical perspective. It argues that the traditional formulation of SJS is seriously incomplete, and discusses alternative ways of completing it. Moreover, it questions the received view on how SJS should be morally justified, by offering arguments against the view that decision making in accordance with this standard extends the patient's opportunities for self-determination. Instead it suggests a virtue-ethical approach according to which the moral point of SJS-based decision making is not to protect the patient's interests , but to express respect for person. The thesis also critically assesses empirical studies according to which surrogates often fail to correctly predict patients? actual treatment preferences. It is shown that such results cannot, for a number of reasons, support the conclusion drawn that surrogates are ill-equipped to make decisions that comply with SJS